Sensitivity Studies of a Low Temperature Low Approach Direct Cooling Tower for Building Radiant Cooling Systems

Recent interest in cooling towers as a mechanism for producing chilled water, together with the evolutionof radiant cooling, have prompted a review of evaporative cooling in temperate maritime climates. The thermal efficiency of such systems is a key parameter, as a measure of the degree to which the system has succeeded in exploiting the cooling potential of the ambient air. The feasibility of this concept depends largely however, on achieving low approach water temperatures within an appropriate cooling tower, at acceptable levels of energy performance. Previous experimental work for a full scale evaporative cooling system has shown that it is possible to produce cooling water at low process approach conditions (1-3 K), at the higher temperatures required in radiant and displacement systems (14-18°C), with varying levels of annual availability in different temperate climate locations. For such conditions, evaporative cooling has the potential to offer an alternative approach for producing chilled water, particularly in temperate climates, where conventional mechanical air-conditioning systems can, for certain buildings, be considered to be an over engineered solution but where passive cooling is insufficient to offset cooling loads. The current paper describes the development of a mathematical model which analysesthe behavior of a low approach open evaporative cooling tower. The model is used to carry out a series of sensitivity studies assessing the performance of the cooling tower subject to various weather and climatic boundary conditions.